1. Field of the Invention
The present invention relates to a circuit breaker with an overcurrent tripping device which operates a time limit tripping by a bimetal and an instantaneous tripping by an electromagnet.
2. Description of the Prior Art
A conventional circuit breaker with an overcurrent tripping device, which is, for example, shown in a Gazette of Unexamined Japanese Utility Model Application Hei 3-19236, is described referring to FIG. 4. FIG. 4 is a sectional side view schematically showing a constitution of the conventional circuit breaker, and especially showing the conventional overcurrent tripping device of the circuit breaker.
As shown in FIG. 4, the conventional circuit breaker comprises a housing 1 made of a resin. The housing 1 consists of a base member 1a and a cover member 1b. A conductor 2, whereon a load current flows, is fixed on the base member 1. An end 2a of the conductor 2 is connected to a known moving contact mechanism (which is not shown in the figure) and the other end 2b is connected to a terminal member 3. A fixed core 4, which has substantially U-letter shaped section in a plane vertical to the paper sheet of FIG. 4, is provided on the conductor 2 for generating a magnetic force by the load current flowing on the conductor 2. A bimetal 5 is fixed to the conductor 2 on an end 5a thereof. An adjustable screw 6 is provided on the other free end 5b of the bimetal 5 in a manner that an end 6a of the screw 6 faces to a trip lever 7. The trip lever 7 is rotatably borne by a pivot 8. An operation arm 9 is rotatably borne by another pivot 11 and has a moving core 10 which is fixed on an end 9b and a pushing part 9a which is formed on the other end 9a for pushing the trip lever 7 when the operation arm 9 rotates in clockwise direction in the figure. An extension spring 12 is provided for supplying a rotation force to the operation arm 9 in a direction to make the moving core 10 separate from the fixed core 4. Another adjustable screw 13 is provided on a fixed part 14 for adjusting a gap between the fixed core 4 and the moving core 10. The above-mentioned pivots 8 and 11 and the fixed part 14 are provided on a frame which is not shown in the figure.
A tripping operation of the above-mentioned conventional circuit breaker with the overcurrent tripping device is described as follows.
When an overload current which is a little larger than a rated current of the conductor 2 flows, the bimetal 5 warps. And thereby, the end 6a of the screw 6 contacts the trip lever 7. As a result, the trip lever 7 rotates in clockwise direction in the figure.
When an overload current which is larger than a predetermined value flows on the conductor 2, the fixed core 4 generates a magnetic attraction force, and the moving core 10 is momentarily attracted to the fixed core 4. Thereby, the operation arm 9 rotates in clockwise direction in the figure. When the operation arm 9 rotates, the end 9a of the operation lever 9 pushes the trip lever 7. As a result, the trip lever 7 rotates in clockwise direction in FIG. 4.
When the trip lever 7 rotates in clockwise direction in the figure, a latch of a tripping device (which is not shown in the figure) is released. And thereby, the conventional circuit breaker is tripped, and the current is cut off.
In the conventional circuit breaker with overcurrent tripping device configured above, since the fixed core 4 and the moving core 10 are respectively fixed on the independent members such as the base member 1a and the frame (not shown in the figure), there are dimensional tolerance limits in the mass-produced parts. Therefore, for making the operation arm 9 to start to rotate by a current of a predetermined value, the gap between the fixed core 4 and the moving core 10 must be adjusted by provision of the adjustable screw 13. Furthermore, since the fixed core 4, the operation arm 9 and so on are respectively held on different independent members, the total size of the overcurrent tripping device becomes larger. And thereby, a larger space is necessary for containing the overcurrent tripping device in the housing 1 of the circuit breaker.